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advent-of-code/2017/day3/day3.erl

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1.3 KiB
Erlang
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2017-12-04 00:02:10 -05:00
-module(day3).
-export([start/0]).
next_largest_square(Target)
-> recurse_next_largest_square(1, Target).
recurse_next_largest_square(X, Target)
when (X rem 2) =/= 0, (X*X) >= Target -> X;
recurse_next_largest_square(X, Target)
-> recurse_next_largest_square(X+1, Target).
position_in_outer_shell(Square, Target)
-> PreviousSquare = (Square - 2) * (Square - 2),
Target - PreviousSquare.
position_on_side(Position, Square)
when Position == 0 -> Square - 1;
position_on_side(_Position, Square)
when Square == 1 -> 1;
position_on_side(Position, Square)
-> Offset = Position rem (Square - 1),
if Offset == 0 -> Square - 1;
true -> Offset end.
distance_to_center(Position, Square)
-> Center = Square div 2,
VertOffset = abs(Center - Position),
Center + VertOffset.
find_distance(Target)
-> Square = next_largest_square(Target),
Position = position_in_outer_shell(Square, Target),
Index = position_on_side(Position, Square),
distance_to_center(Index, Square).
start()
-> io:fwrite("~B ~B~n", [1, find_distance(1)]),
io:fwrite("~B ~B~n", [12, find_distance(12)]),
io:fwrite("~B ~B~n", [23, find_distance(23)]),
io:fwrite("~B ~B~n", [1024, find_distance(1024)]),
io:fwrite("~B ~B~n", [368078, find_distance(368078)]),
io:fwrite("https://oeis.org/A141481/b141481.txt~n").